33 Weeks and doc thinks I may be narrow?

I had my checkup this morning and my little lady has assumed the position and everything looks good. I talked to my doc about the fact that intercourse has become difficult and painful. I don't have a uti or any sort of infection. The doctor said this suggests that I may have a narrow birth canal. She'll check this at my next appointment when they start doing cervical checks but I'm just curious if anyone else has been told this?